Hot Topics:

CU-Boulder: Pine beetles now breeding twice a year instead of just once

By Laura Snider, Camera Staff Writer

Posted:
03/15/2012 10:39:52 AM MDT

Updated:
03/15/2012 09:13:57 PM MDT

A mountain pine beetle. (Courtesy of Jeffry Mitton )

Mountain pine beetles are now breeding twice in some years instead of once, according to researchers at the University of Colorado, contributing to the severity of the current beetle outbreak, which has devastated lodgepole pine forests across the state.

Historically, mountain pine beetles in Colorado laid their eggs in the bark of pines in late July or August. The larvae that emerged from the eggs burrowed deeper into the bark, where they spent the winter. During the warm days of spring, the larvae began to transform into adults, and by late July and August, the beetles flew from their trees, looking for new, un-infested pines to lay their eggs in, repeating the one-year cycle.

Scott Ferrenberg, a graduate student in CU's Department of Ecology and Evolutionary Biology, began to realize that something in the beetle's life cycle was amiss when he saw the insects taking flight at odd times.

Ferrenberg and Mitton, who is also a Camera columnist, teamed up to study the problem. To track the full cycle of one beetle generation, the researchers headed out to CU's Mountain Research Station, 10,000 feet northwest of Nederland, in search of still-healthy lodgepole pines. When the pair identified a tree that had not been attacked by beetles in the previous years, they tagged it.

Advertisement

"Then we would put a lure on those, so the beetles in the area would focus on that tree," Mitton said. "We would perhaps put seven lures on a tree and then watch the trees intently in June."

When the beetles that had over-wintered as larvae emerged from their bark-covered homes in May and June, Mitton and Ferrenberg watched them attack the tagged tree and lay eggs. Then, throughout the summer, the researchers could peel back bits of bark and watch the life cycle play out -- in hyper-speed.

The eggs hatched and the larvae grew into adults in a matter of months, leaving that tree to fly to a new home by August or September.

And since a beetle can lay 60 eggs at once, this could increase the number of beetles attacking the area's lodgepole pine forests by 60 times in one season.

"When we say we are witnessing a summer generation -- we watch it in tree after tree after tree," Mitton said. "We see the data that suggests to us that in a number of other places in the West, they're also having the summer generation."

Ferrenberg and Mitton believe that the ability to create two generations of beetles in one year is linked to warmer springs. At the Mountain Research Station, where the study was conducted, the number of spring days with above-freezing temperatures has increased by 15.1 in the last two decades, giving the young beetles the opportunity to more quickly mature into adults.

The two believe that springs were warm enough to support a second generation of beetles at high elevations in 2008, 2009 and 2010. Last summer, the beetles did not produce a second generation in trees near the Mountain Research Station, but they did at lower elevations.

The fact that beetle behavior is impacted by warming temperatures puts the beetles in good company.

"If you just ask how many insects have been known to respond to climate change, the answer is hundreds," Ferrenberg said.

Among the insects that have changed their behaviors are close relatives of the mountain pine beetle, including spruce beetles. According to the U.S. Forest Service, the spruce beetle infested 262,00 acres of Colorado forests in 2011. And the climate may help explain the severity of that outbreak as well.

"Historically, the spruce beetle needed two to three years for generation," Ferrenberg said. "The majority of its population have gone down to only needing one year for generation. That's leading to an increase in spruce beetles across the West."

Panthers brace for rematch of epic '13 playoff battleAs is typical for high school coaches at this stage of the season, Boulder boys basketball leader Eric Eisenhard didn't waste much time celebrating a big win. Full Story

New coordinator pushes Buffs to work, play at level he expectsJim Leavitt has discovered this much about his new defense at Colorado: He has some talent with which to work, but his players need to put it in another gear. Full Story